1. Field of the Invention
This disclosure is directed toward flat-panel video displays, and is more particularly directed toward improvements in performance, efficiency and manufacturing economy of displays employing electroluminescent polymer materials.
2. Background of the Art
U.S. Pat. Nos. 4,663,559, 5,656,883 and E.P.S. 0.288.616 B1, all to Alton O. Christensen, (Christensen) disclose a true-ohmic, no-barrier, non-tunneling, injecting contact between the low work function metal Cr.sub.3 Si and SiO.sub.2 (silica) as a n-type semiconductor, co-deposited as a cermet. Contact equilibrium accumulates the silica conduction band with electrons. Those electrons are less than 1 eV, typically 0.6 eV from vacuum level. In the present disclosure, that same interface physics is extended to an injecting, non-tunneling ohmic contact obtained between the cermet and n-type polymer semiconductors and electroluminescent (EL) material. That contact at equilibrium injects electrons into the polymer semiconductor conduction band, prohibits tunneling, and permits only minimal hole conduction. The ohmic contact to EL semiconducting polymers allows a third, gate terminal to be effective in controlling avalanche in the semiconductor. The cermet contact to EL polymer blocks hole current flow, increases EL carrier recombination, and improves efficiency and luminous output over prior art tunneling EL.
Polymers woven into fabric are well known. A class of such polymers, consisting of microfibers of micron and sub-micron dimension, is woven into silk-like fabrics. The ability of certain co-polymers to emit light has been known for less than two decades. Selected conjugate or ladder-type polymers may have dielectric, resistive, thermal conductivity, n or p type conductivity and EL properties. Entities presently exploring such polymers include the University of California at Santa Barbara and its cooperating company UNIAX, and Cambridge Display Technology cooperates with Cambridge University's co-polymer work. Christensen Technologies, Inc. funds development of the present invention at North Carolina State University.
All prior art EL polymer displays suffer from at least the following significant properties and deficiencies which affect luminous output, efficiency of EL, reliability, life and economics of manufacture:
(a) EL is generated from diode devices by tunneling though a source-contact barrier. The efficiency of luminescence of the prior art is low, as illustrated in "Carrier Tunneling and Device Characteristics in Polymer Light-Emitting Diodes", J. Appl. Phys. 75, (3), Feb. 1, 1994. PA1 (b) Attempts to increase luminous output by increased field across the barrier, and current through the polymer, causes polymer melting. PA1 (c) Tunneling through the contact barrier causes accumulated stress and change in barrier tunneling parameters, resulting in luminous intensity loss and shortened operating life. PA1 (d) The EL devices are diodes increasing the difficulty of pixel selection and control of luminous intensity. PA1 (e) Deposition and photolithographic definition of EL devices is costly. PA1 (f) The area and pixel density of a display is limited by deposition and photolithography equipment's' capabilities and definition. PA1 (a) a cermet of Cr.sub.3 Si and SiO.sub.2 obtains a vacuum barrier of less than 1 eV, and typically about 0.6 eV with a field applied there across; and PA1 (b) that vacuum barrier is sufficiently low, for cermet in contact with n-type polymer EL and polymer semiconductors, to form an injecting, non-tunneling ohmic contact therebetween.
In view of the above properties and deficiencies of prior EL polymer displays, objects of the present invention are summarized below.
A primary object of the present invention is to provide a woven fabric of semiconductor fibers of electroluminescent (EL), n and p types, together with conductors and insulators, organized in the warp and woof of a weaving loom, to form, interconnect and produce a full color, full function video display of high luminous intensity, definition and area suitable for any video system.
An additional object of the present invention is to create EL by controlled non-destructive avalanche, rather than by tunneling, of carriers in polymer EL semiconductor thereby increasing efficiency and luminous output.
Another object of the present invention is to provide a triode, gated, EL device, and controlling avalanche and luminous intensity by bias potentials supplied to the gate, together with source-drain potentials of the nominal values used in integrated circuits.
Yet another object of present invention is to assure gate control of avalanche EL in an EL device, rather than tunneling of the prior art, by forming a no-barrier, non-tunneling contact between cermet and the EL device source.
Still another object of the present invention is to increase the efficiency of luminous output of an EL device by effect of the cermet source contact which minimizes hole current and increases EL recombination.
Another object of the present invention is to provide a longer, more reliable operating life for an EL device by eliminating the tunneling contact stresses of prior art, and by use of a gate to produce and control the avalanche and luminous intensity.
Still another object of the present invention is to provide manufacturing economies of the textile industry to the manufacture of video displays.
A further object is to weave and interconnect complementary address and other logic devices to provide address and modulation of pixel color and luminous intensity.
There are other advantages and applications of the present invention which will become apparent in the following disclosure to those skilled in the art.